Multilayer thin-walled metal bellows are widely used in different engineering fields, in aircraft industry, engine manufacturing, and oil industry, for example, for securing a movable joint for the pipelines required for compensating their displacement as a result of external actions, in particular.
Different methods for producing the multilayer thin-walled bellows are known. Fabrication of multilayer bellows of separate thin plates by a welding is described in the U.S. Pat. No. 2,797,112 the U.S. Cl. 72-59, 1959. However, the known method is rather laborious and requires additional testing for securing the reliable operation of these bellows.
A method for producing thin-walled bellows is presented in the U.S. Pat. No. 3,782,156 the U.S. Cl. 72-59, 1974. This method consists of preliminary formation of turns on the external and internal surfaces of round billets, treatment of their internal surface by a roller, compaction with the formation of corrugations and heat treatment for the metal stress-relief. But the known technology requires special complicated equipment and much time for producing a bellows.
The USSR Inventor's Certificate No. 1076166 Int. Cl. B 21 D 15/00, 1984 proposes to make bellows by a mechanohydraulic skelping with the formation of ring corrugations on a round billet at subsequent subrecrystallization annealing at a temperature of 680.+-.10.degree. C. This method allowed a reduction of labor input during the fabrication and a raise in the operational reliability of the bellows.
The USSR Inventor's Certificate No. 1292870 Int. Cl. B 21 D 15/00, 1987 describes a method for producing a multilayer thin-walled bellows of stainless steel, including skelping round billets, several runs of each round billet drawing up to a given size, packing the drawn round billets into a multilayer bank, corrugating the bank with the bellows formation as a result and its heat treatment. According to the known method, the round billets are deformed by drawing through the matrix using the punches, their diameter changes, then the billets are inserted one into another, forming the bank, and corrugated with subsequent operations of surface deformation and heat procession--subrecrystallization annealing.
The operation of drawing each round billet before their packing allowed to increase a product quality due to the strength growth at repeated loading.
However, when alloys undergoing structural variations at heating, age-hardenable nickel-based alloys for example, are used as materials for round billets, such deformations as cracks on the billet walls are possible during their drawing and corrugating due to the low ductility of these alloys. Besides, because of the high tendency to oxidation being characteristic to alloys, there is a possibility for having such defects as cracks and faulty fusions in the bellows made of them at their welding with fittings. This fact limits the use of such bellows under the conditions of high temperature, high pressure and corrosive media during a long time period.